1. Field of the Invention
The present invention relates to an image display method and apparatus. More particularly, the present invention relates to an art of dynamically adjusting a contrast and light source luminance in accordance with entered display data in an image display apparatus that is operable to irradiate light from a light source such as a backlight onto a light-receiving display device as represented by a liquid crystal panel, in order to provide a high level of perceptible screen luminance.
2. Description of the Related Art
A prior art concerning the above is disclosed in published Japanese Patent Application Laid-Open No. 1-239589. The prior art provides a unit operable to detect a maximum value of an image signal to permit light such as a light source to be irradiated in proportional to the detected maximum value, thereby reducing electric power consumption.
The term “micro area” as set forth herein refers to a small region of a display screen where the maximum luminance is available. The micro area includes a single pixel or otherwise several pixels. The term “macro area” as given herein refers to a large region of the display screen where bright highlights are available.
However, the prior art has some problems as discussed below.
Problem 1: When a micro area having great luminance is present in the display screen, then it is difficult to obtain beneficial effects of reducing power consumption.
When a micro area having great luminance, such as dotted areas and white characters, is present in the display screen, then the prior art provides control over the light source with reference to such a micro area. As a result, the light source tends to be excessively controlled toward bright illumination. This drawback precludes a reduction in power consumption.
Problem 2: A pure color is insufficient in visual quality.
When color display is made according to the prior art, then a Y-value in YUV signals or an average of RGB values in RGB signals is used as “luminance”. Adjustment is made in accordance with the “luminance”.
Assume that display data having high-saturation (e.g., in a RGB ratio of 0%, 0%, and 80%) in the entire screen is entered. The display data corresponds to nearly solid “blue”. At this time, the YUV signals have a Y-value of 9%, while the RGB signals have a RGB average of 27%.
As a result, according to the prior art, a light source has luminance as small as 9% or 27%, and true “blue” cannot be displayed, even when a signal of “blue” on a display panel has a value as high as, e.g., 100%.
As seen from the above, a problem with the prior art is that a pure color tends to be insufficient in visual quality.
Problem 3: Characteristics inherent to a display device are not reflected.
The prior art takes no account of characteristics inherent to a display device. As a result, it is difficult to obtain desired luminance under severe circumstances in which luminance tends to be insufficient because of a reduction in electric power.